Human tumor necrosis factors α (TNFα) and β (TNFβ, or lymphotoxin) are related members of a broad class of polypeptide mediators, which includes the interferons, interleukins and growth factors, collectively called cytokines (Beutler, B. and Cerami, A., Annu. Rev. Immunol. 7:625-655 (1989)).
Tumor necrosis factor (TNFα and TNFβ) was originally discovered as a result of its anti-tumor activity, however, now it is recognized as a pleiotropic cytokine capable of numerous biological activities including apoptosis of some transformed cell lines, mediation of cell activation and proliferation and also as playing important roles in immune regulation and inflammation.
To date, known members of the TNF-ligand superfamily include TNFα, TNFβ (lymphotoxin-α, LTβ, OX40L, Fas ligand, CD30L, CD27L, CD40L and 4-IBBL. The ligands of the TNF ligand superfamily are acidic, TNF-like molecules with approximately 20% sequence homology in the extracellular domains (range, 12%-36%) and exist mainly as membrane-bound forms with the biologically active form being a trimeric/multimeric complex. Soluble forms of the TNF ligand superfamily have only been identified so far for TNF, LTα, and Fas ligand (for a general review, see Gruss, H. and Dower, S. K., Blood, 85(12):3378-3404 (1995)), which is hereby incorporated by reference in its entirety.
These proteins are involved in regulation of cell proliferation, activation, and differentiation, including control of cell survival or death by apoptosis or cytotoxicity (Armitage, R. J., Curr. Opin. Immunol. 6:407 (1994) and Smith, C. A., Cell 75:959 (1994)).
Mammalian development is dependent on both the proliferation and differentiation of cells as well as programmed cell death which occurs through apoptosis (Walker et al., Methods Achiev. Exp. Pathol. 13:18 (1988). Apoptosis plays a critical role in the destruction of immune thymocytes that recognize self antigens. Failure of this normal elimination process may play a role in autoimmune diseases (Gammon et al., Immunology Today 12:193 (1991)).
Itoh et al. (Cell 66:233 (1991)) described a cell surface antigen, Fas/CD95 that mediates apoptosis and is involved in clonal deletion of T cells. Fas is expressed in activated T cells, B-cells, neutrophils and in thymus, liver, heart and lung and ovary in adult mice (Watanabe-Fukunaga et al., J. Immunology. 148:1274 (1992)). In experiments where a monoclonal Ab to Fas is cross-linked to Fas, apoptosis is induced (Yonehara et al.,J. Exp. Med. 169:1747 (1989); Trauth et al., Science 245:301 (1989)). In addition, there is an example where binding of a monoclonal Ab to Fas may stimulate T cells under certain conditions (Alderson et al., J. Exp. Med. 178:2231 (1993)).
Fas antigen is a cell surface protein of relative MW of 45 Kd. Both human and murine genes for Fas have been cloned by Watanabe-Fukunaga et al., (J. Immunol. 148:1274 (1992)) and Itoh et al. (Cell 66:233 (1991)). The proteins encoded by these genes are both transmembrane proteins with structural homology to the Nerve Growth Factor/Tumor Necrosis Factor receptor superfamily, which includes two TNF receptors, the low affinity Nerve Growth Factor receptor and the LTβ receptor CD40, CD27, CD30, and OX40.
Recently the Fas ligand has been described (Suda et al., Cell 75:1169 (1993)). The amino acid sequence indicates that Fas ligand is a type II transmembrane protein belonging to the TNF family. Fas ligand is expressed in splenocytes and thymocytes. The purified Fas ligand has a MW of 40 kd.
Recently, it has been demonstrated that Fas/Fas ligand interactions are required for apoptosis following the activation of T cells (Ju et al., Nature 373:444 (1995); Brunner et al., Nature 373:441 (1995)). Activation of T cells induces both proteins on the cell surface. Subsequent interaction between the ligand and receptor results in apoptosis of the cells. This supports the possible regulatory role for apoptosis induced by Fas/Fas ligand interaction during normal immune responses.
The polypeptide of the present invention has been identified as a novel member of the TNF ligand super-family based on structural and biological similarities.
The effects of TNF family ligands and TNF family receptors are varied and influence numerous functions, both normal and abnormal, in the biological processes of the mammalian system. There is a clear need, therefore, for identification and characterization of compositions, such as antibodies, that influence the biological activity of TNF receptors, both normally and in disease states. In particular, there is a need to isolate and characterize antibodies that modulate the biological activities of TL5. Such antibodies will be useful for, example, in the treatment of autoimmune disease, graft versus host disease, rheumatoid arthritis, lymphadenopathy, and cancer.